An expansion joint is a small bridge over an expansion gap which is provided between a bridge abutment and a bridge deck, or between two segments of the bridge deck; the small bridge extends beyond the edges of the expansion gap. The expansion gap has a width which changes with the temperature of the structure, and the small bridge of the expansion joint is constructed to adjust its width to accommodate the variations in the width of the gap. The allowable variations in the width of the expansion joint will be referred to herein as its movement rating.
The edges of the upper surfaces of the bridge deck, abutment, or other roadway segments are not always in the same horizontal plane, and they can vary as traffic moves over the structure. These variations can be 0.5 cm or more.
The expansion joint and its anchorage should be constructed to adapt to these conditions, and to resist the effects of traffic, particularly that of heavy vehicles, which are especially destructive when the top of the expansion joint is set at the same level as the roadway.
Various types of expansion joints have been used or proposed. They can be summarized as follows:
The components constituting the mini-bridge can be either a sliding metal element, for example, in a finger joint or a sliding plate joint, or an elastomer joint, or an elastomer honeycomb joint.
The various sliding elements or elements of variable width are fastened either directly or by metal elements, to the roadway of a bridge or to an abutment.
The anchorage itself generally comprises metal bolts fixed in the concrete of the roadway, or rods buried in the concrete. This involves long and delicate work because of the tolerances on the order of millimeters may be required in concrete work, and it is burdensome because of the small amounts of material used at the time of installation of the joint in a previously constructed concrete roadway.
It has been proposed to use thermosetting resins to remedy these drawbacks. For example, it is known to use thermosetting resins to anchor the bolts in concrete. Others have used thermosetting resins to make the edges of the joint, to avoid their erosion by traffic. Also, others have made more advanced proposals such as in French Pat. No. 71/43,203, in which a joint comprising metal slides is simply glued to the roadway structures using resins; this eliminates the need for concrete when joints are installed in a previously-constructed roadway, and thus the problem of supplying small amounts of concrete at the site at that time and the problems caused by slow setting of concrete.
The last-mentioned joint does indeed eliminate fatigue problems. On the other hand, problems arise because of the difference between the expansion coefficients of the resin and concrete, that of the resin being about 10 times higher. Mortar composed of about 20% by weight of resin and 80% aggregate are less of a problem in this respect. However, they nevertheless have coefficients of expansion three to five times higher than that of concrete in the roadway. During temperature variations, these differences lead to stresses at the concrete/resin mortar interface. Since concrete is the more fragile material, it generally cannot support these stresses. These generally produce transverse fissures, and ultimately tearing away of the surface part of the roadway concrete.